> - you would accept patches that make it possible to use the remaining memory> as as raw physical memory.

Correct.

The only people concerned about 2M+ on PC kind of machines tend to bedatabase people, and they are more than happy to just get it as "extramemory" rather than having it around as generic buffers for the page cacheetc.

> The physical memory could be used for ram disks (->swap file), or for other> devices that need lots of memory without kernel support.

Indeed. Note, however, that once you pass 4GB, you have other problems,namely standard PCI DMA doesn't go there, so not all devices would behappy using it.

A RAM-disk always works.

Btw, the RAM-disk approach is what NT does too, for pretty much the samereasons.

> Is someone currently writing such a patch?

Not that I know of.

Note that to access the high memory, you need to use special page tableentries, so there are subtle issues with TLB coherency on SMP systems etc.The only sane way to do it is probably to reserve one 4MB pte per CPU, andallow each CPU to locally have whatever TLB window they want to the highmemory.

Basically it's not hard, but there are subtle issues like the above thatyou have to get right. And while you can test it on a machine with lessthan 1GB of memory, you do generally want to have access to more memoryfor "real" testing.

Linus

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